[PLAT-4237] added gridstructure endpoint for viewports, comments for initial gridstructure GET
[PLAT-4138] moved update viewport method to MainGridViewport subclasses, removed update grid structure
[PLAT-4138] removed grid structure and updates from Analytics Grid
[PLAT-4138] removed grid structure updates
[PLAT-4138] Updating viewports and grid structure using stored state